Monolithic microwave integrated circuits (MMICs) that include low-noise amplifiers (LNAs) and detectors have been used for detecting weak millimeter waves. FIG. 1 is a circuit diagram of an MMIC 300 that includes an LNA and a detector. As illustrated in FIG. 1, millimeter waves that are received by an antenna 301 are amplified by an LNA 302 and are converted to direct current (DC) voltages by a detector 303. The DC voltages are output from an output terminal 304 as voltage Vdet.
The detection sensitivity of millimeter waves by the MMIC 300 is affected significantly by the detector 303. Although Schottky-type diodes are typically used for the detector 303, it has been difficult to obtain adequate detection performance when the bias is approximately 0 V.
A backward diode, which is a type of a tunnel diode, is capable of high-frequency detection and mixing.
Japanese Patent Laid-open No. 2000-114551, Japanese Patent Laid-open No. 09-331025, and Japanese National Publication of International Patent Application No. 2003-518326 are examples of related art documents.